High temperature resins based on poly((cyclohexylene-dimethylene) terephthalate) possess desirable chemical resistance, processability and heat resistance. This makes them particularly well suited for demanding high performance automotive and electrical/electronics applications.
The ability of a substance to retain its shape when subjected to changes in temperature, which is defined as the dimensional stability, is a crucial parameter for many applications. Dimensional stability may be quantified by, for example, the coefficient of linear thermal expansion (CLTE).
Also important in parts made of thermoplastics are mechanical properties such as for example a) the stiffness of the material which is quantified by the modulus of elasticity (E-modulus) corresponding to a proportional constant between stress and strain, the stress at yield and the stress at break, as well as b) the impact strength which is quantified by charpy (un)notched impact.
A good balance between mechanical properties and dimensional stability is particularly important for precision molded articles. Most polymers can be mixed with fillers to provide an almost unlimited range of compositions to fit a wide range of engineering applications. In an attempt to improve mechanical properties, it has been the conventional practice to add various reinforcements to the resin, like for example glass fibers, glass flakes, carbon fiber, mica, wollastonite, talc, calcium carbonate. Glass fibers are known to offer excellent dispersion in high temperature thermoplastic polymers and lead to good mechanical properties under standard conditions. According to the current need of developing highly efficient reinforced polymer for engineering applications demanding improved dimensional stability and good mechanical properties, non-fibrous glass flakes are also used due to the benefits that are: a) a reduced warpage, b) an improved dimensional stability, c) a reduced anisotropy of shrinkage and mechanical properties, and d) high impact properties compared to mineral agents. Examples of glass fiber or glass flakes reinforced poly(alkylene terephthalate) resin compositions can be found in and EP1452567, WO2005/026258, JP06065481 or JP06016914 for poly(cyclohexylene-dimethylene)terephthalate compositions and in U.S. Pat. No. 6,512,027, U.S. Pat. No. 6,180,251 and EP712899 for poly(butylene terephthalate) (PBT) compositions.
Unfortunately, at elevated temperature, thermoplastics filled with conventional glass fiber filler or glass flakes either exhibit reduced dimensional stability and/or inferior mechanical properties such as stiffness, impact resistance and/or aging resistance.
There is a need for a high performance polyester polymer, like for example poly((cyclohexylene-dimethylene) terephthalate) composition having improved dimensional stability at high temperature and retaining a good degree of mechanical properties.